Relevance The relevance of this research to public health lies in its focus on understanding and ameleorating problems of posture and gait control leading to debilitating freezing of gait episodes in persons with Parkinson's disease. Project Summary/Abstract The long-term objectives of this research are to investigate the mechanistic basis and provide evidence in support of the effectiveness of physical therapy interventions for posture and gait disorders in persons with advancing Parkinson's disease (PD). In this exploratory project, we propose to assess the feasibility of a novel therapeutic approach involving posture assisted locomotion (PAL) training to enhance step initiation and gait performance and reduce the incidence of freezing of gait (FOG) in PD. The specific aims are: 1) to compare the effects of a novel PAL training approach with other more widely used physical therapy approaches involving sensory cueing and task practice on step initiation and gait performance in individuals with PD. The outcome measures to be assessed include: 1) incidence, timing, and magnitude of anticipatory postural adjustments (APAs) that precede stepping; 2) step initiation timing and distance; 3) gait speed, cadence, and stride length. Assessments will occur at baseline, after six weeks of training, and at one month and three months post-training; 2) to assess whether step training can reduce the incidence of FOG by comparing FOG frequency before, at the mid-point and immediately after training, and at one month and three months post- training. 3) to explore whether training induced changes in step initiation performance are accompanied by alterations in central motor excitability during the preparation for stepping. Motor preparation will be assessed by comparing elctromyographic, kinetic, and kinematic profiles of the postural adjustment-stepping sequence evoked by an acoustic startle stimulus during the period of motor preparation for voluntary stepping. [unreadable] [unreadable]